1. Field of the Invention
This invention is directed to a method of reducing the moisture content level in waste material by utilizing the combustion gases produced by the combustion of waste material to reduce the moisture content during the preparation of the moisture bearing material for grinding, and to provide an inert atmosphere during the drying and grinding process.
2. Description of the Prior Art
The problem in connection with prior attempts to burn moisture bearing material is that the wetness or moisture content of such material needs to be greatly reduced so it will be amendable to grinding to a size that will be suitable for feeding to a circulating fluid bed combustor (CFB). In some waste material, the moisture content can be as much as about 15 percent. This is the situation found in a mixture of coal containing clay, slate and other particulate. That mixture when it contains up to fifteen percent free moisture will plug mills used to grind the solids. However, when the material has its moisture content lowered to a state of about six percent, it can be utilized in a furnace. Another class of waste material called sludge usually has a moisture content of 60 to 70 percent and usually is a mixture of paper and wood with moisture up to 70 percent. That class of material will plug a mill when attempting to grind the mass in order to reduce the solids to a burnable particulate size.
The drying step is expensive and requires additional equipment. This fact introduces a problem of handling moisture bearing fuel material so it will be amendable to grinding to a particle size that will be suitable for feeding to a circulating fluid bed combustor. There is a further problem in that the grinding of wet material causes a condition of rapid wear to apparatus that is expensive to replace.
When a drying step is employed using an external source of heat energy such as gas or oil, that heat source must be properly cleaned so as to meet local and state environmental standards with a resultant loss of energy that needs to be used to evaporate the moisture.